Title: Solar cell, solar cell with interconnection sheet attached and solar cell module.Abstract: Disclosed are a solar cell, a solar cell with interconnection sheet attached, and a solar cell module wherein a surface of an electrode for first conductive type is covered with a migration suppressing layer for preventing a metal forming electrode for first conductive type from precipitating, and at least one of a surface of migration suppressing layer covering electrode for first conductive type and a surface of electrode for second conductive type is covered with an insulating member. ...

TECHNICAL FIELD

The present invention relates to a solar cell, a solar cell with interconnection sheet attached and a solar cell module.

BACKGROUND ART

In recent years, particularly from the view point of protection of the earth environment, expectation for solar cells that convert sunlight energy into electric energy as a next-generation energy source has been rapidly increased. While various types of solar cells including those using a compound semiconductor and those using an organic material are known, solar cells using silicon crystals are the current mainstream.

The solar cells that are most widely produced and on the market at present have such a structure that an n electrode is formed on the surface where the sunlight enters (light-receiving surface), and a p electrode is formed on the surface opposite to the light-receiving surface (back surface).

For example, Patent Literature 1 (Japanese Patent Laying-Open No. 2005-310830) discloses a back electrode type solar cell wherein an n electrode and a p electrode are formed only on the back surface of the solar cell while no electrode is formed on the light-receiving surface of the solar cell.

CITATION LIST
Patent Literature

PTL 1: Japanese Patent Laying-Open No. 2005-310830

SUMMARY

OF INVENTION
Technical Problem

By the foregoing back electrode type solar cell having the constitution as disclosed in Patent Literature 1 alone, available electric energy is limited. For this reason, a method of electrically connecting a plurality of back electrode type solar cells of the above constitution to form a solar cell module is considered.

Here, as a method of electrically connecting a plurality of back electrode type solar cells to form a solar cell module, there is proposed a method of making a solar cell module by sealing solar cells with interconnection sheet attached having a back electrode type solar cell disposed on an interconnection sheet, in a sealant.

In the following, referring to schematic sectional views of FIG. 12(a) and FIG. 12(b), one example of the aforementioned method of fabricating a solar cell module by sealing the solar cells with interconnection sheet attached in a sealant will be described.

First, as shown in FIG. 12(a), a solar cell with interconnection sheet attached is fabricated by making a back electrode type solar cell 80 and an interconnection sheet 100 adhere with each other by an insulating adhesive 116.

Here, in a solar cell with interconnection sheet attached, an electrode for first conductive type 6 that contacts a first conductive type impurity diffusion area 2 on the back surface of a semiconductor substrate 1 of back electrode type solar cell 80 is disposed on a wiring for first conductive type 12 formed on an insulating base material 11 of interconnection sheet 100, and an electrode for second conductive type 7 that contacts a second conductive type impurity diffusion area 3 on the back surface of semiconductor substrate 1 of back electrode type solar cell 80 is disposed on a wiring for second conductive type 13 formed on insulating base material 11 of interconnection sheet 100.

Here, a light-receiving surface of semiconductor substrate 1 of back electrode type solar cell 80 is formed with a texture structure, and an antireflection film 5 is formed on the texture structure. Here, on the back surface of semiconductor substrate 1 of back electrode type solar cell 80, a passivation film 4 is formed.

Next, as shown in FIG. 12(b), the solar cell with interconnection sheet attached that is fabricated in the manner as described above is sandwiched between a transparent substrate 17 implemented, for example, by a glass substrate having a sealant 18 such as ethylene vinyl acetate, and a back film 19 such as a polyester film having sealant 18, and back electrode type solar cell 80 forming the solar cell with interconnection sheet attached is sealed in sealant 18, and thereby a solar cell module is fabricated.

According to the above method, a plurality of back electrode type solar cells 80 can be electrically connected only by disposing back electrode type solar cell 80 on interconnection sheet 100, so that a solar cell module can be produced more efficiently.

In the solar cell module produced in the manner as described above, there is sometimes the case that potential differences arises between electrodes and between wirings of different conductive types during use of the solar cell module, and a migration (ion migration) phenomenon occurs by an electric field caused by the potential differences.

In the aforementioned solar cell module, since the distance between neighboring electrode for first conductive type 6 and electrode for second conductive type 7 and the distance between neighboring wiring for first conductive type 12 and wiring for second conductive type 13 are short, the metal that forms the electrodes or the wirings precipitates between neighboring electrode for first conductive type 6 and electrode for second conductive type 7, and between neighboring wiring for first conductive type 12 and wiring for second conductive type 13, and then moves to lower the insulation resistance, which may deteriorate characteristics of the solar cell module. Hence, amelioration of this is desired.

In consideration of the above circumstances, it is an object of the present invention to provide a solar cell, a solar cell with interconnection sheet attached and a solar cell module capable of preventing characteristics of the solar cell module from deteriorating.

Solution to Problem

The present invention relates to a solar cell including: a semiconductor substrate; a first conductive type impurity diffusion area and a second conductive type impurity diffusion area formed on one surface side of the semiconductor substrate; an electrode for first conductive type disposed on the first conductive type impurity diffusion area; and an electrode for second conductive type disposed on the second conductive type impurity diffusion area, wherein a surface of the electrode for first conductive type is covered with a migration suppressing layer for preventing a metal forming the electrode for first conductive type from precipitating, and at least one of a surface of the migration suppressing layer covering the electrode for first conductive type and a surface of the electrode for second conductive type is covered with an insulating member.

In this case, in the solar cell according to the present invention, each of the migration suppressing layer and the insulating member is disposed to traverse a straight line connecting neighboring the electrode for first conductive type and the electrode for second conductive type.

Further, the present invention relates to a solar cell with interconnection sheet attached including: a solar cell; and an interconnection sheet, wherein the solar cell has a semiconductor substrate, a first conductive type impurity diffusion area and a second conductive type impurity diffusion area formed on one a surface side of the semiconductor substrate, an electrode for first conductive type disposed on the first conductive type impurity diffusion area, and an electrode for second conductive type disposed on the second conductive type impurity diffusion area, the interconnection sheet has an insulating base material, a wiring for first conductive type and a wiring for second conductive type disposed on the insulating base material, the electrode for first conductive type of the solar cell is disposed to be electrically connected with the wiring for first conductive type of the interconnection sheet, the electrode for second conductive type of the solar cell is disposed to be electrically connected with the wiring for second conductive type of the interconnection sheet, a surface of the electrode for first conductive type is covered with a migration suppressing layer for preventing a metal forming the electrode for first conductive type from precipitating, and at least a part of a surface of the solar cell between neighboring the electrode for first conductive type and the electrode for second conductive type, and at least a part of a surface of the insulating base material between neighboring the wiring for first conductive type and the wiring for second conductive type are joined by an insulating member.

In this case, in the solar cell with interconnection sheet attached according to the present invention, each of the migration suppressing layer and the insulating member is disposed to traverse the straight line connecting neighboring the electrode for first conductive type and the electrode for second conductive type.

Further, the present invention relates to a solar cell with interconnection sheet attached including: a solar cell; and an interconnection sheet, wherein the solar cell has a semiconductor substrate, a first conductive type impurity diffusion area and a second conductive type impurity diffusion area formed on one surface side of the semiconductor substrate, an electrode for first conductive type disposed on the first conductive type impurity diffusion area, and an electrode for second conductive type disposed on the second conductive type impurity diffusion area, the interconnection sheet has an insulating base material, a wiring for first conductive type and a wiring for second conductive type disposed on the insulating base material, the electrode for first conductive type of the solar cell is disposed to be electrically connected with the wiring for first conductive type of the interconnection sheet, the electrode for second conductive type of the solar cell is disposed to be electrically connected with the wiring for second conductive type of the interconnection sheet, a surface of the wiring for first conductive type is covered with a migration suppressing layer for preventing metal forming the wiring for first conductive type from precipitating, and at least a part of a surface of the solar cell between neighboring the electrode for first conductive type and the electrode for second conductive type, and at least a part of a surface of the insulating base material between neighboring the wiring for first conductive type and the wiring for second conductive type are joined by an insulating member.

In this case, in the solar cell with interconnection sheet attached according to the present invention, each of the migration suppressing layer and the insulating member is disposed to traverse the straight line connecting neighboring the wiring for first conductive type and the wiring for second conductive type.

Further, the present invention relates to a solar cell module including the solar cell of the solar cell with interconnection sheet attached according to any of the above descriptions sealed in a sealant.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a solar cell, a solar cell with interconnection sheet attached and a solar cell module capable of preventing characteristics of the solar cell module from deteriorating.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of one example of a solar cell module of the present invention.

FIGS. 2(a) to 2(h) are schematic sectional views illustrating one example of a production method of a back electrode type solar cell used in a solar cell module of the present invention.

FIGS. 3(a) and 3(b) are schematic plan views of one example of the back surface of a back electrode type solar cell used in a solar cell module of the present invention.

FIGS. 4(a) to 4(d) are schematic sectional views illustrating one example of a production method of an interconnection sheet used in a solar cell module of the present invention.

FIG. 5 is a schematic plan view of one example of an interconnection sheet used in a solar cell module of the present invention.

FIGS. 6(a) and 6(b) are schematic sectional views illustrating one example of a production method of a solar cell with interconnection sheet attached of the present invention.

FIG. 7 is a schematic sectional view of another example of a solar cell module of the present invention.

FIGS. 8(a) to 8(d) are schematic sectional views illustrating another example of a production method of an interconnection sheet used in a solar cell module of the present invention.

FIG. 9 is a schematic plan view of another example of an interconnection sheet used in a solar cell module of the present invention.

FIGS. 10(a) and 10(b) are schematic sectional views illustrating another example of a production method of a solar cell with interconnection sheet attached of the present invention.

FIG. 11 is a schematic sectional view of another example of a solar cell module of the present invention.

FIGS. 12(a) and 12(b) are schematic sectional views illustrating one example of a method of making a solar cell module by sealing a solar cell with interconnection sheet attached in a sealant.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be described. In the drawings of the present invention, the same reference numeral denotes an equivalent part or a corresponding part.

Embodiment 1

FIG. 1 is a schematic sectional view of one example of a solar cell module of the present invention. In the solar cell module having a constitution as shown in FIG. 1, a solar cell with interconnection sheet attached having a back electrode type solar cell 8 disposed on an interconnection sheet 10 is sealed in a sealant 18 such as ethylene vinyl acetate between a transparent substrate 17 such as a glass plate and a back film 19 such as a polyester film.

Here, back electrode type solar cell 8 includes a semiconductor substrate 1, a first conductive type impurity diffusion area 2 and a second conductive type impurity diffusion area 3 foamed on the back surface of semiconductor substrate 1, an electrode for first conductive type 6 formed in contact with first conductive type impurity diffusion area 2, and an electrode for second conductive type 7 formed in contact with second conductive type impurity diffusion area 3.

A light-receiving surface of semiconductor substrate 1 of back electrode type solar cell 8 is formed with a concavo-convex structure such as a texture structure, and an antireflection film 5 is formed to cover the concavo-convex structure. A back surface of semiconductor substrate 1 of back electrode type solar cell 8 is formed with a passivation film 4.

Also a migration suppressing layer 20 is formed to cover the surface (lateral wall 6a and bottom face 6b) of electrode for first conductive type 6 on the back surface of back electrode type solar cell 8, and migration suppressing layer 20 is formed to cover the surface (lateral wall 7a and bottom face 7b) of electrode for second conductive type 7.

In this example, first conductive type impurity diffusion area 2 and second conductive type impurity diffusion area 3 are formed into strip shapes, respectively extending on the front surface side and/or back surface side of the paper plane of FIG. 1, and first conductive type impurity diffusion area 2 and second conductive type impurity diffusion area 3 are arranged alternately at a predetermined interval on the back surface of semiconductor substrate 1.

In this example, also electrode for first conductive type 6 and electrode for second conductive type 7 are formed into strip shapes, respectively extending on the front surface side and/or back surface side of the paper plane of FIG. 1, and electrode for first conductive type 6 and electrode for second conductive type 7 are formed respectively in contact with first conductive type impurity diffusion area 2 and second conductive type impurity diffusion area 3 along first conductive type impurity diffusion area 2 and second conductive type impurity diffusion area 3 on the back surface of semiconductor substrate 1 through an opening provided in passivation film 4.

On the other hand, interconnection sheet 10 includes an insulating base material 11, a wiring for first conductive type 12 and a wiring for second conductive type 13 formed into predetermined shapes on the surface of insulating base material 11.

Wiring for first conductive type 12 on insulating base material 11 of interconnection sheet 10 is formed into a shape that mutually faces electrode for first conductive type 6 on the back surface of back electrode type solar cell 8 one by one.

Wiring for second conductive type 13 on insulating base material 11 of interconnection sheet 10 is formed into a shape that mutually faces electrode for second conductive type 7 on the back surface of back electrode type solar cell 8 one by one.

In this example, also wiring for first conductive type 12 and wiring for second conductive type 13 are formed into strip shapes, respectively extending on the front surface side and/or back surface side of the paper plane of FIG. 1.

Then, by adhesion of back electrode type solar cell 8 and interconnection sheet 10 by insulating member 16, a solar cell with interconnection sheet attached is formed.

Here, in the solar cell with interconnection sheet attached, electrode for first conductive type 6 of back electrode type solar cell 8 is disposed so that it is electrically connected with wiring for first conductive type 12 of interconnection sheet 10 with migration suppressing layer 20 interposed therebetween, and electrode for second conductive type 7 of back electrode type solar cell 8 is electrically connected with wiring for second conductive type 13 of interconnection sheet 10 with migration suppressing layer 20 interposed therebetween.

At least part of the back surface of back electrode type solar cell 8 between neighboring electrode for first conductive type 6 and electrode for second conductive type 7, and at least part of the surface of insulating base material 11 between neighboring wiring for first conductive type 12 and wiring for second conductive type 13 are joined by insulating member 16.

In the following, one example of a production method of a solar cell module having a configuration shown in FIG. 1 will be described. In the following, after describing a method of forming back electrode type solar cell 8 first, a method of forming interconnection sheet 10 will be described, and subsequently, a method of forming a solar cell with interconnection sheet attached by adhesion between back electrode type solar cell 8 and interconnection sheet 10, and lastly, a method of forming a solar cell module will be described. In the present invention, the order of forming back electrode type solar cell 8 and interconnection sheet 10 is not particularly limited.

First, as shown in a schematic sectional view of FIG. 2(a), semiconductor substrate 1 having a slice damage 1a formed on the surface of semiconductor substrate 1 is prepared, for example, by slicing from an ingot. Here, as semiconductor substrate 1, for example, a silicon substrate formed, for example, of polycrystalline silicon or monocrystalline silicon of either n conductive type or p conductive type may be used.

Next, as shown in a schematic sectional view of FIG. 2(b), slice damage 1a on the surface of semiconductor substrate 1 is removed. Removal of slice damage 1a may be achieved, for example, by etching the surface of the silicon substrate after slicing with mixed acid of a hydrogen fluoride aqueous solution and nitric acid or an alkaline aqueous solution such as sodium hydroxide, when semiconductor substrate 1 is formed from the aforementioned silicon substrate.

Here, while the size and the shape of semiconductor substrate 1 after removal of slice damage 1a are not particularly limited, thickness of semiconductor substrate 1 may be, for example, 50 μm or more, and 400 μm or less, and particularly preferably about 160 μm.

Next, as shown in a schematic sectional view of FIG. 2(c), first conductive type impurity diffusion area 2 and second conductive type impurity diffusion area 3 are respectively formed on the back surface of semiconductor substrate 1. Here, first conductive type impurity diffusion area 2 may be foamed, for example, by a gas-phase diffusion using gas containing first conductive type impurities, and second conductive type impurity diffusion area 3 may be formed, for example, by a gas-phase diffusion using gas containing second conductive type impurities.

Here, first conductive type impurity diffusion area 2 is not particularly limited insofar as it is an area containing first conductive type impurities, and exhibiting either an n conductive type or a p conductive type. As the first conductive type impurities, when the first conductive type is an n type, n type impurities such as phosphorous, for example, may be used, whereas when the first conductive type is a p type, p type impurities such as boron or aluminum, for example, may be used.

Impurity diffusion area for second conductive type 3 is not particularly limited insofar as it is an area containing second conductive type impurities and exhibiting a conductive type opposite to that of first conductive type impurity diffusion area 2. Here, as the second conductive type impurities, when the second conductive type is an n type, n type impurities such as phosphorous, for example, may be used, whereas when the second conductive type is a p type, p type impurities such as boron or aluminum, for example, may be used.

The first conductive type may be either an n conductive type or a p conductive type, and the second conductive type may be a conductive type opposite to the first conductive type. That is, when the first conductive type is an n type, the second conductive type is a p type, and when the first conductive type is a p type, the second conductive type is an n type.

As the gas containing first conductive type impurities, when the first conductive type is an n type, gas containing n-type impurities such as phosphorous, for example, POCl3 may be used, and when the first conductive type is a p type, gas containing p-type impurities such as boron, for example, BBr3 may be used.

As the gas containing second conductive type impurities, when the second conductive type is an n type, gas containing n-type impurities such as phosphorous, for example, POCl3 may be used, and when the second conductive type is a p type, gas containing p-type impurities such as boron, for example, BBr3 may be used.

Next, as shown in a schematic sectional view of FIG. 2(d), passivation film 4 is formed on the back surface of semiconductor substrate 1. Here, passivation film 4 may be formed by a thermal oxidation method or a plasma CVD (Chemical Vapor Deposition) method.

Here, as passivation film 4, for example, a silicon oxide film, a silicon nitride film, or a stack of a silicon oxide film and a silicon nitride film may be used, however, any film that is stable as an insulating substance may be used without limited to these.

Thickness of passivation film 4 may be, for example, 0.05 μm or more and 1 μm or less, and particularly preferably about 0.2 μm.

Next, as shown in a schematic sectional view of FIG. 2(e), after forming a concavo-convex structure such as a texture structure on the entire surface of the light-receiving surface of semiconductor substrate 1, antireflection film 5 is formed on the concavo-convex structure.

Here, the texture structure may be formed, for example, by etching the light-receiving surface of semiconductor substrate 1. For example, when semiconductor substrate 1 is a silicon substrate, the texture structure may be formed by etching the light-receiving surface of semiconductor substrate 1 using an etching solution heated to a temperature of 70° C. or more and 80° C. or less, prepared, for example, by adding isopropyl alcohol to an alkaline aqueous solution of sodium hydroxide or potassium hydroxide.

Antireflection film 5 may be formed, for example, by a plasma CVD method. As antireflection film 5, for example, a silicon nitride film may be used without limitation.

Next, as shown in a schematic sectional view of FIG. 2(f), by removing a part of passivation film 4 of the back surface of semiconductor substrate 1, a contact hole 4a and a contact hole 4b are formed. Here, contact hole 4a is formed to expose at least part of the surface of first conductive type impurity diffusion area 2, and contact hole 4b is formed to expose at least part of the surface of second conductive type impurity diffusion area 3.

Each of contact hole 4a and contact hole 4b may be formed, for example, by a method of forming a resist pattern having openings in the parts corresponding to the sites where contact hole 4a and contact hole 4b are to be formed, on passivation film 4 using a photolithography technique, and then removing passivation film 4 through the openings of the resist pattern by etching or the like, or a method of applying an etching paste on parts of passivation film 4 corresponding to the sites where contact hole 4a and contact hole 4b are to be formed, followed by heating to remove passivation film 4 by etching.

Next, as shown in a schematic sectional view of FIG. 2(g), after forming electrode for first conductive type 6 that contacts first conductive type impurity diffusion area 2 through contact hole 4a, and electrode for second conductive type 7 that contacts second conductive type impurity diffusion area 3 through contact hole 4b, migration suppressing layer 20 is formed to cover the surface (lateral wall 6a and bottom face 6b) of electrode for first conductive type 6 on the back surface of back electrode type solar cell 8, and migration suppressing layer 20 is formed to cover the surface (lateral wall 7a and bottom face 7b) of electrode for second conductive type 7.

Then as shown in a schematic sectional view of FIG. 2(h), by disposing insulating member 16 to cover migration suppressing layer 20 covering the surfaces of electrode for first conductive type 6 and electrode for second conductive type 7, back electrode type solar cell 8 is fabricated.

When back electrode type solar cell 8 is connected with interconnection sheet 10 as will be described later, insulating member 16 shown in FIG. 2(h) may not be formed, or alternatively, insulating member 16 may be formed only on the surface of passivation film 4 between neighboring electrode for first conductive type 6 and electrode for second conductive type 7. In these cases, it is possible to prevent insulating member 16 from entering between an electrode and a wiring to inhibit electric connection, in electrically connecting electrode for first conductive type 6 of back electrode type solar cell 8 and wiring for first conductive type 12 of interconnection sheet 10, or in electrically connecting electrode for second conductive type 7 of back electrode type solar cell 8 and wiring for second conductive type 13 of interconnection sheet 10.

Here, as electrode for first conductive type 6 and electrode for second conductive type 7, electrodes made of a metal such as silver may be used, however, the metal is not particularly limited to silver.

As migration suppressing layer 20, a layer capable of preventing precipitation of a metal that forms electrode for first conductive type 6 and/or a metal that forms electrode for second conductive type 7 may be used, and for example, a layer formed of an oxide, a compound or an alloy containing at least one kind of a metal selected from the group consisting of tin, palladium, gold, platinum, chromium, iron, nickel and lead may be used. Migration suppressing layer 20 may be a monolayer or may be made up of a plurality of layers.

Migration suppressing layer 20 may be formed by firing after applying a conventionally known cream solder by a method such as screen printing, dispenser application or inkjet application.

Height of each of electrode for first conductive type 6 and electrode for second conductive type 7 may be, for example, 5 μm or more and 50 μm or less, and particularly preferably about 15 μm.

FIG. 3(a) is a schematic plan view of one example of the back surface of back electrode type solar cell 8 fabricated in the manner as described above is shown. Here, on the back surface of back electrode type solar cell 8, each of electrode for first conductive type 6 and electrode for second conductive type 7 is formed into a strip shape, and a strip of electrode for first conductive type 6 and a strip of electrode for second conductive type 7 are arranged alternately one and one at an interval. Each of the lateral wall and the bottom face of electrode for first conductive type 6, and each of the lateral wall and the bottom face of electrode for second conductive type 7 are covered with migration suppressing layer 20. Then, insulating member 16 is disposed to cover the entire back surface of back electrode type solar cell 8.

For example, in FIG. 3(a), when electric power from back electrode type solar cell 8 is derived from the left end of electrode for first conductive type 6 and the right end of electrode for second conductive type 7 rather than from the entire bottom face 6b of electrode for first conductive type 6 or from the entire bottom face 7b of electrode for second conductive type 7, insulating member 16 may be once disposed on the entire back surface of back electrode type solar cell 8, and then insulating member 16 positioned in a site where electric power is derived may be removed, to enable electric connection with the electrode.

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